In the manufacture of hollow glassware having flat bottoms and/or relatively flat face portions, articles of simple form, such as culinary glassware, are usually shaped by simply pressing a parison of melted glass between a matrix and a die. However, when the shape becomes hollower and more complex, it is necessary to operate in at least two stages. In the "pressed-blown" process, a rough is first formed by pressing, then the final form is obtained by blowing in a finishing mold; this process makes it possible to obtain objects with a rather large neck, such as industrial vessels. For the manufacture of flasks or bottles, one ordinarily has recourse to the "blown-blown" process wherein the parison is injected into a mold in which it is formed into a prerough by formation of the ring at the lower part, the orifice constituting an entry for blowing. The mold is then completed by a base mold, and the prerough is transformed into a rough by blowing in the roughing mold thus constituted. The rough is turned over, suspended by its ring and finished to a final form by a second blowing in a finishing mold. This requires the use of thick glass, causes alignment problems and results in the formation of a visible seam.
These processes all form glass articles in a slow, progressive fashion with the so-formed articles having relatively thick wall thicknesses of at least about 100 mils and more often at least about 125 mils. For many applications, these relatively heavy wall thicknesses are unnecessary resulting in a high cost of manufacture due to both the thickness of the glass and relative slowness of the process.
A significant improvement in the act has been the development of the ribbon process. Ribbon blown glass envelopes have been traditionally formed on a ribbon machine with two-part molds having a partible construction and which rotate while encircling a hollow molten glass blank. Said conventional glass molds have been generally provided with a paste coating of the central mold cavity along with vent openings to form a steam cushion against which the glass envelope is blown while said mold halves are rotating. Although the bulb portion of a glass envelope blown in the conventional manner has included cylindrical as well as conical and spherical shapes, all of these shapes have terminated at the closed end of the bulb portion in a spherical contour preventing the blown article from physically supporting itself. Accordingly, such limitation has retarded any wider utilization of conventional ribbon blown glass envelopes in a variety of end product applications including liquid containers and even lamp glass envelopes requiring a relatively flat face portion to serve as a lens member in the lamps.
The present invention relates to novel means whereby glass articles of various types are blown on a ribbon machine in a novel mold construction which shapes the closed end of the glass envelope to provide a self-supporting base contour wherein all structural features of said articles are a unitary, integral construction and wherein the wall thickness thereof is substantially less than that found in conventional pressed glass articles. More particularly, said novel mold construction includes three basic parts which cooperate in forming a bulb shape terminating in a flattened contour sufficient to permit the glass envelope to be self supporting, that is to stand alone without additional physical support. The basic mold design of the present invention includes a pair of cooperative partible halves forming the sides of the blown glass envelope in a central cavity and which further includes a separate base part located at the lower end of said cavity to shape the closed end of said blown glass envelope into the desired self-supporting contour, said base part of the mold being provided with reciprocal motion in a vertical direction.
Accordingly, an important object of the present invention is to provide a ribbon blown glass envelope of a unitary, integral construction having assorted shapes for various end product applications wherein the bulb portion of said envelope terminates in a self-supporting contour and wherein the wall thickness of the envelope is substantially less than that found in conventional pressed glass envelopes.
Another important object of the present invention is to provide ribbon blown glass envelopes having either curved or planar sides together with an integral self-supporting base contour which can also be planar or curved in shape.
Still another important object of the present invention is to provide an improved method for manufacutre of said novel glass envelope on a ribbon machine by means of a novel mold design.